DIY hovercraft guide - BR6
Video filmed in a small space - you can see the excellent maneuverability of the hovercraft, but neither its acceleration nor its top speed.
Better video coming soon.
First, if you don't know much about hovercrafts, I strongly recommend you to read this short text that explains a bit of theory.
It is recommended to read the whole guide before starting, so you can anticipate the next steps as you go along. Feel free to enlarge the pictures by right-clicking on them and select "open in a new tab" or "display image".
Here is the list of needed components. The links redirect to Hobbyking.com, Masterairscrew.com and Retif.eu where you can purchase some of them.
RC components & tools
- a 40 cm servo extension cable (or several shorter cables connected together to get a similar length)
- a soldering gun and solder
- a drill and a 5 mm bit
- a 3 mm thick polypropylene plate (must be perfectly flat, at least 50 cm long by 50 cm large, density 600g/m² or more)
- a lollipop stick (3 mm diameter)
- 70 cm of synthetic thread (polyester sewing thread, for example)
- a piece of wire mesh, 38 cm long by 18 cm large (the meshes can have a size of 10-15 mm)
- a large garbage bag, something resistant but not too thick
- a piece of cardboard at least 13 cm long by 18,5 cm large
- a few packing bubbles (see pictures at the end of the build to see the required dimensions)
Let's start with the hovercraft hull. Cut a polypropylene plate 50 cm long by 25 cm large. The polypropylene channels must be lengthwise.
Each time you cut a polypropylene piece, you can deburr the edges to get a smoother finish.
Draw four dots, each one being at 7,5 cm from both edges of the hull. Draw two lines to connect the dots as shown. These two lines measure 35 cm long and are separated by 10 cm.
With a screw, drill three holes on each line, one at the center and the others at 2,5 cm from both ends of the line.
Cut two polypropylene strips 35 cm long by 2,5 cm large - again the channels must be lengthwise. Put them aside, we will use them later to set the skirt under the hovercraft.
The side on which you draw the two lines is the underside of the hovercraft. Turn the hull over to work on the top.
In the center of the hull, at 1,5 cm from one of the edges, draw a 92 mm long by 65 mm large rectangle.
Cut three sides of the rectangle as shown on the picture.
Using a non-sharp tool, strongly mark the last uncut side of this rectangle to break the polypropylene channels, then fold this piece.
You obtain the flap we talked about earlier : it will deflect part of the air towards the skirt.
Cut a 22 cm long by 8 cm large polypropylene plate, with the channels lengthwise. This is the motor support.
At 6,4 cm from the edges of the motor support, draw two straight lines and strongly mark them with a non-sharp tool. Then fold this piece.
Screw the motor support from below the hull, above the air deflector flap. Note that no screw should overlap on the two 35 cm lines you have drawn previously.
For all the steps of this build, please use your longest screws by default (from 3,5 cm to 4 cm) unless you are told otherwise.
Let a space of 1 cm between the rear of the hovercraft and the rear of the motor support (see next picture).
Fold the air deflector flap to bring it as close as possible to the motor support. Then screw the flap to the motor support with a screw on each side.
Add duct tape on the top, right and left of the air deflector flap to get an airproof compartment.
Solder two electric wires to the motor (around 50 cm each to be sure you have enough, you can cut the excess later).
I made a huge mistake purchasing single stranded electric wires, much less flexible, leading to terrible soldering. The HobbyKing link above will redirect you to the correct wires.
Put the propeller adaptor and the propeller on the motor axis. The Master Airscrew propeller I use here has a very thin shaft that I extended to 5 mm by carefully drilling it, but as this propeller is top of the line, it is worth the effort.
The propeller must be well wedged on its adaptor : if necessary, widen the propeller shaft, or on the contrary, add a shim to reduce its diameter.
To prevent injuries and damage, double check if the propeller is firmly attached on the motor shaft.
Cut two pieces of piano wire, 25 cm long. Make three turns with the piano wire around the two motor mounting screws.
In the end, the piano wire must be in a V-shape, forming a 50° angle (next picture shows it better). You should get a total length of around 8 cm of piano wire under the motor, and around 15 cm on the sides.
Fold the piano wire at 90° so that it is parallel to the motor axis. For the wires under the motor, fold at 2 cm from the screw. For the sides, fold at 3,5 cm from the screw. Work the wires until everything is folded correctly and as straight as possible - on the picture, this step is not finished yet.
This is a difficult step. Take your time and don't hesitate to start over if you get a bad result.
Finally, pay attention to the length of the two mounting screws : they should be long enough to hold the piano wire to the motor, but if you cannot turn the propeller manually without encountering any resistance, it means they're too long.
Pre-perforate the motor support in the four spots indicated with a straight rod of piano wire, then slowly insert the four "legs" of the motor into the motor support.
The entire length of the motor must be laid flat on the motor support, and the shaft must land right in the center. If you get a different result, the piano wire may be bent incorrectly, and you have to work them again to get a better result.
There should be a 5 mm gap between the hull and the propeller when it is oriented vertically.
At the back of the motor support, on the sides, there should be a few extra centimeters of piano wire. Leave 1 cm and cut the rest. Bend the two rods inside the motor support like shown.
Drill two holes in the motor support at the rear of the motor to pass the thickest of your cables ties. Tighten it around the motor, then cut off the excess. Be careful not to tighten it too much, otherwise the motor support may deform in the long term.
The attachment of the cable tie should ideally be inside the motor support, and not outside as you can see here on the left : it will create a bit of drag.
If you have not done it yet, add electrical tape or heat shrink tubes to insulate the solders between the motor and the wires.
We continue with super-gluing the servo behind the motor. The servo arm should be aligned, or almost aligned, with the motor axis. Finer adjustment can be done later using the radio trim.
The servo arm will actually point the other way, towards the rear, as you will see on the next pictures.
Connect the servo extension cable and the servo to the appropriate channels on your receiver. As I have a 4-way radio set, my servo connects to "aileron channel", and my extension cable connects to "elevator channel". By default, check your radio manual to know what to do. Put the receiver into bubble wrap and tape it on the air deflector flap, while the antenna can be taped on the hull, next to the motor support.
Pass the two electric wires inside the polypropylene plate, like shown on the picture, not too close to the motor support.
Note : some receivers must be re-binded regularly with the ESC because of some kind of weird incompatibility. If you fear that you might need to access your receiver regularly, it will be easier to put it in the battery compartment at the front of the hovercraft. If you do so, you will need another ESC cable to connect the servo to the receiver.
Close the back of the motor support with a small polypropylene plate (channels lengthwise for smoother finish). It is important to put the screws in the top of the plate, as shown on the picture, and not on the sides.
Also add two screws from the underside of the hull into this small plate. This will correct the deformation that usually appears at the rear of the hull after folding the air deflector flap.
There should be no need to access the receiver again during the assembly if you have made the correct connections for the servo and the ESC cable.
Cut two polypropylene pieces, 10 cm length by 7 cm height, with the channels heightwise. These are the steering flaps.
Take the lollipop stick and cut two pieces of 1 cm, they will be used to set the flaps to the correct height.
Cut two pieces of piano wire, respectively 38 cm and 14 cm length, and fold them in a U shape so the top rod measures 9,5 cm. The longest one will contain the two flaps spindles and the shortest one will be the flaps synchronisator.
Work these U shapes until the rods are as straight as possible - again, at this point, I still had some work to do.
Add duct tape on the front of the flaps to make them a bit more aerodynamic.
Using a rod of piano wire, pierce a hole on both sides in the last polypropylene channel of the motor support (one of the next pictures shows it a lot better).
Set the spindles into the 10th channels from the front of the flaps, add a piece of lollipop stick and push everything into the motor support. Then, set the flaps synchronisator in the last channel of both flaps.
To make sure the flaps synchronisator stays in place, pass a piece of synthetic thread through the last channel of one flap and knot it around the synchronisator at 2 cm from the flap.
Smear the knot with super glue to secure it, then cut the thread excess when the glue has dried. It isn't necessary to repeat this step on the other side.
Connect the flaps to the servo using two pieces of synthetic thread, each 25 cm long.
To get a good balance between angle of rotation and torque, I passed the threads in the 4th hole from the center of the servo arm, but other settings can be better - check this video to see a bit of theory about "control link geometry".
Drill two holes in each flap, just behind the spindles, at the height of the servo arm. Pass the threads through the holes and make two very tight knots. Smear them with a bit of super glue and let dry for a few hours, then cut the excess.
The flaps are finished. This is a side view of the left one.
You can see the spindle inserted in the last polypropylene channel of the motor support and the two holes where you pass the threads before knotting them.
Take the two polypropylene strips you cut earlier (35 cm long by 2.5 cm large) and screw them under the hovercraft through the six holes previously drilled, using 2,5 cm long screws.
The strips must be screwed exactly on the lines you have drawn at the beginning.
Cut a rectangle of wire mesh 38 cm long by 18 cm wide, then fold it to get the shape shown of the picture : 16 cm height at the back, a width of 5 cm, and 17 cm at the front : fold this extra centimeter as shown on the picture.
Make the necessary cutouts at the back of the wire mesh to allow the motor support and motor to pass through.
Round the top of the wire mesh by cutting a few meshes (from 9 cm height, cut 1 cm towards the center every 2 cm of height).
Using a polypropylene reinforcement, screw the front of the wire mesh into the two polypropylene strips below the hovercraft.
These two screws should be located around 14,5 cm from the rear of the hovercraft.
Use your smaller screws (2,5 cm long) for this step.
The rear of the wire mesh can be joined with the "motor legs" using small cable ties.
Use a few duct tape tabs to stick the bottom of the wire mesh to the bottom of the motor support - that was not done yet when I took the picture, but it is absolutely necessary.
Then, check if the wire mesh is firmly held in place.
Pass the servo extension cable through a mesh, as far as possible from the propeller (you can see it on the left) and secure it with a bit of tape.
Complete the propeller protection with a polypropylene strip of 6,2 cm width and 48 cm length (channels lengthwise for better aesthetics). To give it the shape of the wire mesh, make a first fold at 11,5 cm from one edge, make another one 5,5 cm further, then 13 cm further and again 5,5 cm further. Screw this protection from below the hull with two screws on each side.
The center of gravity of the BR6 must be located not exactly in the middle of the hovercraft, but rather between 22 and 22,5 cm from the rear. You need to define where your battery should be located for the hovercraft to be correctly balanced.
When you have defined the place where your battery must be located, drill two holes to take out the electric wires previously inserted in the hull channels. Mines are at 15 cm from the front because I will use a heavy NIMH battery (which I do not recommend at all). These holes will be drilled elsewhere if you use a lighter LIPO battery.
Congratulations for making it so far. As you can see, your BR6 is already looking great at this point.
Time to deal with the electronics. As you go along with this step, make sure to use electrical tape or heat shrink tubes to insulate the soldered connections.
I recommend using XT-60 connectors which seem to be the best compromise (Tamiya can't withstand a lot of amps, and XT-30 are usually too small compared to the battery wires). If your battery came with a different female connector, you can replace it (video tutorial here).
The ESC should mention "motor" on one side and "battery" on the other. Solder the two electrical wires from the motor to the ESC (tutorial here) and solder the male connector on the other side. Finally, connect the ESC to the radio receptor using the servo extension cable.
Check if your ESC jumpers are correctly set for a LIPO battery. Turn on your transmitter and set the throttle to zero, then connect the battery to the ESC. If you use a Turningy ESC, the motor should beep once to confirm the good electrical and radio links (it's not common, but sometimes the receiver needs a new manual binding, check your radio manual to see the procedure).
You can now test the propeller and the flaps, as a reward for your work until now. Be careful : even without a skirt, your hovercraft will tend to take off and move forward :-)
In case the servo works in the opposite direction to that expected, there should be a "reverse" button on your radio transmitter.
Make a "box" that will contain the battery, the wires and the ESC and screw it from below the hull. A cover will then be screwed on top of this box to protect electronics from the water.
This "box", and the battery it contains, should be positioned so that the center of gravity of the hovercraft is 22 - 22,5 cm from the rear. My heavy NIMH battery will be positionned at 11 cm from the front, but you will have a different positioning with a lighter LIPO battery.
The result I obtained here isn't pretty nor clever - I will not be able to connect / disconnect the battery without unscrewing the cover first. You can get a better result by doing things differently and by adding a power switch.
Check out Mr Raynal's original pictures for another design.
Take the trash bag and cut it out to flatten it completely.
Print this file on A4 paper and reproduce the shape on a cardboard piece.
Use this cardboard piece to cut out two pieces of skirt from the trash bag using the measures indicated (25,1 cm at the top and 10,1 cm at the bottom).
These pieces will be the front and the rear of the skirt.
The sides of the skirt have exactly the same corners, but are longer : 50,1 cm at the top and 35,1 cm at the bottom.
Here are the four pieces of the skirt. You now need to solder these parts together with a soldering gun.
Use a wooden workbench for this step.
Take a short piece and a long piece of skirt. Put one on top of the other so that the corners match.
Take the cardboard piece and set it 1 mm before the corner. With your soldering gun, slowly follow the shape of the cardboard. The two skirt pieces will melt and solder.
Let cool for 20 seconds, then gently remove the skirt pieces that will certainly be sticked both to the workbench and to the cardboard.
It is possible that you do not get a good solder on your first try. If you see any holes in the corner, make a second pass with your soldering gun. If it's not enough, it is recommended to start over with new pieces of trash bag. You may also need to use a new soldering tip to get maximum heat.
In the same way, solder the four corners together to complete the skirt. Then turn it over like a sock, so that the solders are on the inside, for strength and aesthetics.
The "inner rectangle" in the center of the picture should measure 35 cm long by 10 cm wide, while the "outer rectangle" should measure 50 cm long by 25 cm wide.
You will now tape the skirt under the hull. It is imperative to take your time to do this correctly (up to an hour) to make sure everything is airproof and waterproof.
Remove the battery from its compartment and put the hovercraft upside down. If you respected the dimensions of the wire mesh and the polypropylene protection mentioned above, your BR6 can also stand on its right and left sides without being damaged. Do what feels most comfortable to you.
On the picture, you are facing the rear of the hovercraft, with the air deflector flap being in the upper right corner. At the center, you can see two of the four screws that hold the polypropylene protection around the wire mesh.
Tape the "outer rectangle" of the skirt to the hull, edge to edge. Start by taping two corners to tighten one side of the skirt, then add tape along the length. Do the same for the remaining sides, taping one corner at a time. This is certainly the most difficult step of the build : you will have to work in a smaller and smaller space as you tape the skirt.
It is also possible to tape the skirt on the upperside of the hovercraft - but as the tape will be visible on the upperside of the hull, the finish will be much worse.
Use double-sided tape to stick packing bubbles to the hull on the right and left sides of the hovercraft.
You can skip this step if the hovercraft is intended to be used only on dry land.
For this step, it would be perfect if you could find this kind of long cylinder shaped bubbles, at the center of the picture.
You can then "close the skirt" by taping the right and left sides on the two polypropylene strips, edge to edge. Tape the ends first to tighten the skirt, then add tape along the strips.
Cut a 10 cm piece of duct tape. In its middle, stick another 5 cm piece of duct tape, so you get only two sticky parts of 2,5 cm at the extremities.
This piece of tape will keep the back of the skirt from vibrating and tearing. It must keep the skirt in place without hindering its inflation. It is not useful to do the same at the front.
It is possible that some water gets inside the rear of the skirt when you operate it on water. Drill three holes at the rear of the skirt, so that the water that would have entered can flow out.
You can skip this step if the hovercraft is intended to be used only on dry land.
Turn everything on and set the throttle to the maximum to check if the skirt inflates well everywhere and if the back of the skirt does not vibrate. If it does, cut the piece of tape and place another in a different way. Also check if the hovercraft seems well balanced - if not, your battery may be positioned a little too far to the right or to the left.
Your BR6 is now finished. Congratulations on your work to build this RC hovercraft. Before operating your BR6 on water, I recommend that you give it a first try in a bathtub.
When not in use, keep your BR6 with a wedge under the motor support to avoid any deformation of the hull on the long-term.
The skirt is perfectly suited to smooth floors such as tiles or concrete slabs. Beware of rougher surfaces such as tar which can damage it. The skirt remains replaceable if necessary.
The best way to improve this RC hovercraft would be using a brushless motor and a brushless ESC to have more motor power while reducing power consumption. As the motor dimensions will be slightly different, maybe you should be able to lower the height of the motor support, the mesh and the polypropylene protection. The garbage bag skirt can be replaced by a k-way fabric skirt, whose pieces can be sewn together. This skirt will be more resistant to rough surfaces.
It is possible to make a bigger BR6 using a bigger propeller and adjusting all dimensions and components proportionally. Finally, if you are interested in making a derivative of the BR6, with a motor for the propulsion and another motor dedicated to the skirt inflation, check the pictures of the Qoum 9 that may give you a few ideas.
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